Power converters include items such as solar power inverters, charging systems for electric vehicles (EV), converters used in wind turbines, power supplies for electronics, and others. Generally, they are used to convert direct current (DC) power to alternating current (AC) power, or AC power to DC. In many types of power converters, for example those using pulse width modulation, a relatively fast (typically 2-20 KHz) modulation frequency is required in order to keep the total harmonic distortion (THD) within regulated limits. These fast switching speeds lead to significant switching losses in the transistors that affect overall conversion efficiency. These losses result in heat generation in the transistors, often leading to thermal cycling that reduces the lifetime of the electronics.
One prior-art approach improves the total harmonic distortion from a single converter by controlling the firing angle of a pulse-width modulated (PWM) sequence, as discussed in US Patent Publication No. 2013/0033907. One can also interleave the firing angles from multiple inverters in the solar power case to generate low harmonic current using minimal active/passive filters as discussed in US Patent Publication No. 2009/0283129. Another approach uses active current injection by a grid operator to reduce harmonics, as disclosed in U.S. Pat. No. 5,345,375.
However, other approaches with higher conversion efficiency and longer electronics lifetime are desirable.